nervous system 3 - action potentials

Question 1

different phases of the action potential

Answer 1

1 - resting potential
2 - rising phase (depolarise)
3 - falling phase (repolarise)
4 - undershoot (more hyperpolarised)

Question 2

voltage gated sodium channel

Answer 2

closed at rest (-65mV).
depolarisation to -40mV causes conformational change, opening pore
Na+ moves across conc gradient into cell, depolarises as positive ions entering negative side of membrane

Question 3

when do all sodium channels open

Answer 3

-40mV

Question 4

inactivated state vs closed state on voltage-gated Na+ channels

Answer 4

inactivated - ‘gate’ blocks open channel
closed - after inactivated, channel fully closes

Question 5

what happens at peak depolarisation

Answer 5

Na+ channels close

Question 6

voltage gated K+ channels during action potential

Answer 6

closed at rest. require depolarisation to open. delay (1ms) in open. allow hyperpolarisation.

Question 7

what is the time where and excitable cell is unable to generate a subsequent action potential - two types?

Answer 7

refractory period:
absolute refractory period
relative refractory period (action potential chance lower due to hyperpolarisation)

Question 8

what channels are open at point 3 - just after peak depolarisation where repolarisation begins

Answer 8

Na+ channels inactivate
K+ channels open

Question 9

where is there a high concentration of sodium channels

Answer 9

axon initial segment

Question 10

what influences conduction velocity

Answer 10

resistance of membrane - less resistance on larger axons
sodium channel density

Question 11

what is the name for action potential propagation along myelinated axons

Answer 11

saltatory conduction

Question 12

what are the gaps between myelin sheaths

Answer 12

nodes of ranvier

Question 13

where are ion channels in myelinated axons?

Answer 13

very few under myelin, high concentrations in nodes of Ranvier

Question 14

why can myelinated axons produce more efficient action potential propagation

Answer 14

node-to-node communication like a domino effect. passive depolarisation to next node opens Na+ channels on node 2

Question 15

largest diameter myelinate axons- name and function

Answer 15

A-alpha
proprioceptors of skeletal muscle

Question 16

second largest diameter myelinated axons- name and function

Answer 16

A-beta
mechanoreceptors of skin

Question 17

smallest diameter myelinated axons- name and function

Answer 17

A-delta
pain, temperature

Question 18

smallest unmyelinated axons - name and function

Answer 18

C
temperature, pain, itch

Question 19

stretch, bend or pressure sensitive unmyelinated fibres?

Answer 19

mechanoreceptors

Question 20

gating which depends on stretch of surrounding membrane?

Answer 20

mechanosensitive ion channels

Question 21

name for areas of skin that tile the surface of the body linking specific areas of the skin with specific spinal nerves

Answer 21

dermatomes

Question 22

amino acid neurotransmitters examples

Answer 22

glutamate (excitatory)
aspartate (inhibitory)
main neurotransmitters found in CNS

Question 23

monoamines neurotransmitters examples

Answer 23

dopamine, noradrenaline, adrenaline, histamine, serotonin

Question 24

all classes of neurotransmitters

Answer 24

amino acids
monoamines
peptides
others (e.g. acetylcholine)

Question 25

synthesis and storage of neurotransmitters

Answer 25

enzymes synthesised in cell body, transported along axon, synthesise neurotransmitters, pack into vesicles, neurotransmitter released into synaptic cleft, component parts after breakdown taken up into presynaptic terminal, enzyme synthesises back into neurotransmitter.

Question 26

which channels are present in pre- synaptic terminal

Answer 26

voltage gated calcium channels

Question 27

sequence of events leading up to neurotransmitter release?

Answer 27

action potential reaches presynaptic terminal depolarising membrane and opening voltage gated calcium channels, vesicles bind to Ca2+ channels then release neurotransmitters

Question 28

vesicles cycle

Answer 28

vesicle binds to membrane, Ca2+ entry triggers fusion of vesicle (exocytosis), new vesicle membrane pinched off, forms new vesicle and is filled with neurotransmitters again.

Question 29

fast response post synaptic receptors?

Answer 29

ionotropic receptor. ion channels open when neurotransmitter binds

Question 30

slow response post synaptic receptors

Answer 30

metabotropic receptors. activation of a second messenger
neurotransmitter binding activates G-protein, alpha subunit of G protein translocates and interacts with something else

Question 31

what determines whether a synapse is excitatory or inhibitory

Answer 31

which neurotransmitter is released

Question 32

effect of excitatory/inhibitory neurotransmitters

Answer 32

excitatory - depolarise towards threshold
inhibitory - hyperpolarise away from threshold

Question 33

which channels open in inhibitory postsynaptic control (IPSP)

Answer 33

chloride (which is negative therefore more hyperpolarised, further from threshold)

Question 34

convergence of synaptic inputs?

Answer 34

tens to thousands of presynaptic neurons input into one neuron

Question 35

spacial summation?

Answer 35

summation of EPSPs generated at different synapses

Question 36

temporal summation?

Answer 36

summation of EPSPs generated at same synapse

Question 37

what does EPSP stand for? which channels open?

Answer 37

excitatory post synaptic potential. Na+ channels

Question 38

what happens when there is an inhibitory input closer to the soma than an excitatory input on the same dendrite

Answer 38

inhibitory suppresses exhibitory

Question 39

agonist vs antagonist

Answer 39

agonist - mimics effect of endogenous neurotransmitter
antagonist - blocks effect of endogenous neurotransmitter

Question 40

what can mimic GABA

Answer 40

ethanol
barbiturates
neurosteriods